Control means for signal control transmission systems



Dec. 22, 1936. H. D. NEWTON 2,065,344

' CONTROL MEANS FOR SIGNAL CONTROL TRANSMISSION SYSTEMS Filed Feb. 1,1933 4 K E w E E {:1

m0 300 700 /000 2500 3000 CYCLES Ff SECUIVD I MlPl/T 1E if 24 25Inventor.- Harold Dnewton.

H is Attorngy.

Patented Dec. 22, 1936 UNITED STATES PATENT- OFFICE CONTROL MEANS FORSIGNAL CONTROL TRANSMISSION SYSTEMS Harold D. Newton, Westmont, N. J.,assignor to General Electric Company, a corporation of New YorkApplication February 1, 1933, Serial No. 654,643 8 Claims. (01. 179-1)The present invention relates to means for quency responsecharacteristic of said system varying the frequency responsecharacteristic of may be varied between wide limits and by a single anelectric signal transmission system, whereby control means.

- signals'transmitted therethrough may be attenu- It is a commoncharacteristic of known freated Within desired and variable frequencyquency response control systems, that attenuation 5 rangeg of or changein the frequency response character- Means for varying the frequencyresponse istic of the system is accompanied by a change incharacteristic of signal transmission systems are the apparent overalloutput volume as registered well known and at present are appliedgenerally by the listening ear. In certain other cases, there 10 toaudio frequency amplifiers as tone control may be an actual change inthe amplitude of the 10 means adapted to accentuate the amplificationsignals transmitted through the system to which in selected portions ofthe audio frequency rethe tone control means is applied, as the tonesponse range of such amplifiers. For this reason control means isvaried. For example, certain the present invention will be hereindescribed by known forms of tone control means having a tone Way ofexample, more particularly in its applicacontrol adjustment whereby thehigh frequency tion to audio frequency amplifiers, although it end ofthe audio frequency range is attenuated is not necessarily limitedthereto. to a greater extent than the middle and lower fre- In the usualaudio frequency amplifying sysquency ranges, provided also a noticeableaccomtem, the tone control means include circuit net panying reductionin the apparent volume of the s works and circuit elements therein foreifecting signal as reproduced by a suitable output device. withinlimits a, desired change in, or adjustment It has been found, however,that a frequency of, the sound frequency transmission or audiofreresponse control system embodying the invention,

' quency response. characteristics of the system, substantially entirelyobviates the above dewhereby the electrical or sound output therefromscribed undesirable characteristics of tone conmay be modified inaccordance with a predetertrol means heretofore employed, whereby thefre- '25 mined frequency response characteristic curve quency responsecharacteristic of the system to to produce a pleasing tone quality froma suitable which it is applied may be Va d Without appreoutput device.ciably affecting the overall amplitude of signal In radio receivingapparatus, the tone control waves transmitted through said system.arrangement in connection with an audio fre- In accordance Wi h t einvention, a W de ran e 30 quency amplifier is such that the audiofrequency of tone control is obtained by providing in consignals from asound producing device, such as nection with an audio frequencytransmission a loud speaker, for example, are increased or decircuit orchannel, means providing shunt paths creased within certain portions ofthe audio frehaving impedance values so related to each other 5 quencyrange, whereby the reproduced sound and to that of said transmissioncircuit or chanmay be made pleasing to the ear under various nel, thateach is adapted to attenuate signals in conditions of reception. v aselected audio frequency range, with substan- Tone control systemsheretofore employed in tially equal individual shunting effect on thecirradio receiving apparatus and the like are characcult, and byproviding a control means having 40 terized by the fact that only alimited range of substantially no frequency response character- 40operation is usually obtainable, or when arranged. istic arranged toincrease gradually the controlfor a wide range of audio frequency tonecoinling effect of the one shunt path while decreasing pensation,require a plurality of control devices. the controlling effect of theother.

It is, therefore, a primary object of this in- By properly relating thecircuit impedance vention to provide an improved frequency responvaluesof the controlling means, the transmission sive tone control systemhaving a relatively wide circuit and the attenuating means, it has beenrange of control. It is a further object of this found that the controlmay be effected throughout invention to provide an improved audiofrequency the frequency range with substantially constant tone controlsystem which embodies a simple cirsignal amplitude or constant volume ofthe sound m cult and a minimum number of circuit elements, output. 1 andwhich may be applied to existing signal The novel features which areconsidered chartransmission systems at low cost. acteristic of theinvention are set forth with par- It is a still further object of thepresent in ticularity in the appended claims. The invention vention toprovide an improved control circuit itself, however, both as to itsorganization and 5 for a signal transmission system, whereby the freitsmethod of operation, together with additional objects and advantagesthereof, will best be understood from the following description taken inconnection with the accompanying drawing, in which:

Figure 1 is a circuit diagram showing a portion of the signaltransmission circuit of an audio frequency amplifier provided with atone control system embodying the invention; Fig. 2 shows curvesillustrating certain operating characteristics of the amplifier shown inFig. 1; Fig. 3 is a circuit diagram'showing a modification of the tonecontrol system of Fig. 1; and Fig. 4 shows a detail modification of thecircuit shown in Fig. 3.

Referring to Fig. 1, an electron discharge amplifier device I is coupledto a suitable source of audio frequency currents represented by asuitable input transformer 2. The electron discharge device I isconnected to a second electrorr discharge amplifier device 3 through asuitable signal transmission circuit, which in the present exampleincludes an audio frequency interstage coupling transformer 4, having anoutput lead 5 which is connected to thegrid of the electron dischargedevice 3, and a return lead 6 which is connected to the cathode of theelectron discharge device 3 through a by-pass capacitor I. The grid ofthe electron discharge device 3 is biased by a potential derived from asuitable source such as a resistor 8. An output choke coil I0 and acoupling capacitor 9 are arranged in the output or anode circuit of thedevice 3 to supply output signals to a suitable translating device suchas a loudspeaker ll. Any suitable output circuit may however be employedto couple the tube 3 to the loudspeaker. The loudspeaker ll representsany suitable sound producing device which may be connected in the outputcircuit of the discharge device 3 for receiving the signals and forcon-. verting them into audible sounds. In the present example, audiofrequency signalssupplied by the input device 2 are amplified by theelectron discharge device I and are transmitted through the transformer4 and the transmission circuit 5, 6 to the electron discharge device 3.

Connected in shunt with the signal transmission circuit 5-6 is a circuitnetwork, or tone control system, including means for variablyattenuating a portion of the frequency range of signals to betransmitted by said circuit. In the present example this includes animpedance device l2, the impedance of which varies with the frequency ofthe applied currents, and which may comprise a fixed capacitor havinglow capacity connected with the transmission circuit, preferably at thehigh potential side 5, and a .series variable resistance provided by apotentiometer iii, the movable contact l4 of which is preferablyconnected with the low potential side 6 of the transmission circuit, allas indicated.

It will be seen that variation of the series resistance by operating themovable arm or contact l4 along the resistor element of thepotentiometer l3 will cause the effectiveness of the impedance device orshunt capacity provided by the condenser I2, to be varied. When themovable contact I4 is moved to a position adjacent to or at one terminalto which the capacitor I2 is connected, it will be seen that the latter.is most effective in providing a shunt path across the transmissioncircuit and serves to attenuate signals above a certain predeterminedfrequency depending upon its capacity value and its relative shuntimpedance value in the circuit 5-6.

The capacitor l2 may have a capacitance such that its impedance tohigher audio frequency signals is relatively low with respect to that ofthe transmission circuit impedance within that range, and thepotentiometer l3 or its equivalent resistance, may have a maximumimpedance value such that when fully in circuit with the capacitor l2,the effectiveness of the latter as a circuit shunting means issubstantially nil. The network or system whereby a desired change in thetone or frequency transmission characteristic of a circuit withoutappreciably changing the resistance load of the transmission circuit, orthe volume or amplitude of the signals transmitted therethrough may beeffected is completed by an impedance, in the present example, aninductor l5, connected in shunt across the signal transmission circuit56, also through the potentiometer means l3, and, through said potentiometer means, in shunt also with the reactancc device l2. The effectof this circuit arrangement is to provide a substantially constant shuntre- 7 sistance load, but having an adjustable impedance, across thesignal transmission circuit 5-6 at all times.

The tone control means or circuit thus provided operates to attenuatesignals in the higher frequency range when the adjustable contact 14 ofthe potentiometer is moved toward the left in the direction of thecapacitor [2, and operates to attenuate signals in the lower frequencyrange when the contact I4 is moved toward the right in the direction ofthe inductor l5; while in the intermediate positions substantially equalparallel paths are provided which attenuate only in some degree signalsin both the high and low frequency ranges. The attenuation of the highor low frequency signals is due to the change in the effectiveness ofthe shunt impedance l5 and the capacitor [2 when the potentiometer armI4 is shifted to the right or left of the intermediate position.

This tone control means or network may be connected across either of thewindings of the transformer 4 by properly proportioning the componentparts thereof in accordance with-the circuit in which it is to be used.The tone control means now includes a circuit providing a high frequencypath and a low frequency path connected together by an element having nofrequency characteristic. The impedance values in each shunt path arepreferably such that each path provides the same resistance load on thetransmission circuit whereby thechange from the one to the other byoperation of the potentiometer device l3 produces no appreciable changein the overall apparent output volume of signals delivered from thesystem. The resistance of the potentiometer I3 is of a value whichpermits but a slight amplitude reduction in the normal frequencycharacteristic of the transformer or signal channel when the adjustablecontact I5 is at the midpoint on the potentiometer l3.

Reference may now be made to Fig. 2 which shows a response curve inwhich per cent of response is plotted against frequency in cycles persecond. Curve A illustrates the frequency characteristic of theamplifier shown in Fig. 1 as measured across the circuit 55 of thesecondary winding of the transformer 4 without the tone control means.Curve B shows the attenuation of the treble or high frequency signalswhen the potentiometer arm I4 is at the left extremity of therein mayreturn to the device l8. Audio frequency signals are applied to deviceI8 through a suitable input or coupling device 20 and the output oftransmission circuit l6l1 is connected with output translating device 2|through a suitable coupling device 22.

In the present example, audio frequency signals applied through thetransformer 20 are amplified by the electron discharge device l8 and aretransmitted to the translating device 2| through the transmissioncircuit |6-l1 and the coupling device 22. Any suitable audio frequencyresponse means may be connected to the transformer 22 such as a soundproducing device 2| shown in connection with said transformer forreceiving the signal output from the transmission circuit Iii-I1 and forconverting the same into audible sounds. This device may be preceded byany desired degree of amplification, as is well understood. Furtherdescription of the amplifier circuit is believed to be unnecessary as itrepresents any suitable signal transmission circuit and is included inan audio frequency amplifier only by way of example as adaptedalso tothis modification of the invention.

'I'h'esignal transmission circuit l8-I| is provided with a tone controlnetwork or means including an impedance device 23, the impedance ofwhich varies with the frequency of the applied currents and a secondimpedance member 24 having no frequency characteristic, all connectedwith one side of the transmission circuit I 6, and a potentiometer 25arranged therebetween and having a movable contact 26 connected to theother side of the transmission circuit l1. As the movable contact arm 26is moved to the right to include resistance in circuit with theattenuating device 23, it causes resistance to be removed from circuitwith the resistor 24 until finally .the resistor 24 is connected inshunt with the transmission circuit Iii-l1 and the attenuating device 23is rendered ineffective. Likewise, when the potentiometer arm is movedto the left to the opposite position at the other extreme end of thepotentiometer element the resistor 24 is rendered substantiallyineffective as a shunt means across the circuit while the device 23 isfully effective. The resistor M is of such a value that it may provideacross the circuit iii-ll substantially the same shunt impedance atallfrequencies in the range to be transmitted, as does the device 23 inthe range of frequencies to be attenuated The effect of this circuitarrangement is to provide substantially a constant impedance in shuntacross the signal transmission circuit for all positions of theadjustable tone control means, by reason of the fact that the variableresistor M is substituted at one end of the control range for the 18,the lead 16 being the paths singly, such paths being composed of theimpedance devices 23 and 24 and portions in circuit therewith of the.resistance element of the potentiometer element 24.

In order that the signal potential output through the transmissioncircuit Hi-l1 may be made substantially constant, or the apparent out-,put volume may be substantially constant, as determined by listening tothe output of the sound producing device 2 I, or be made to vary fromsuch constant output in any desired way, or by way of correction ofcertain undesired responsecharacteristics, the resistor 24 is madevariable, whereby its impedance value may be changed or adjusted withrespect to that of the device 23.

With a variable control means of this character, the tone of the outputmay bevaried by adjustment of the contact 26, and the effect of suchtone adjustment upon. the volume or the apparent volume, as measured bylistening to the sound producing device 2|, may be, adjusted byadjustment of the resistor 24. The resistor 24 may be fixed when onceadjusted to a desired value, as determined by measuring the'amplitude ofthe signal response in circuit l6- -l'1 or by listening to or measuringthe output of the sound producing device 2 I.

The resistor is adjusted to a value such that asan impedance device inthe signal transmission circuit it is substantially equal to thereactance device in the frequency range for which the reactance deviceis effective as an attenuating means. The potentiometer is of such totalre- 'sistance value that by its operation, sufficient resistance may beinserted in .circuit with the reaudio frequency transmission circuit.Likewise,

the tone control system shown may be followed by amplifying means otherthan the sound producing device 2|.

- In connection with the attenuation of signals at frequencies in otherranges, any suitable impedance means may be inserted in place of device23 of Fig. 3. For example, referring to Fig. 4{ a choke coil orimpedance 2! may be substituted, with or without other change in thecircuit. In the present example, no other change is made and theimpedance device is connected in circuit with the potentiometer 25 inthe same manner as the capacitor 23 in Fig. 3. In this case, however, as

is obvious, the choke coil provides a relatively high impedance at theupper or high frequency end of the audio frequency range and adecreasingly lower impedance toward the lower end of the range.Accordingly, when connected by operation of the control contact 26,whereby it is most effective across the circuit lit-ll, it serves toattenuate the lower frequency end of the audio frequency range.

From the foregoing description it will be seen that in accordance withthe invention, and as a preferred embodiment thereof, a tone controlsystem embodying the invention includes a reactance device or circuitimpedance devic-e having an impedance which varies with variations inthe frequency of currents which are caused to pass through it, and suchdevice is connected with a signal transmission channel substantially inparallel with a second impedance device. The effective impedance valuesreduced to terms of load resistances are equal but in differentfrequency ranges whereby they are controllable by a common potentiometermeans having no frequency characteristic, thereby maintainingsubstantially a constant load on the signal transmission circuit.

My invention provides a tone control for accentuating the amplificationof any selected range of frequencies with substantially constant. loadand volume output therefore irrespective of the adjustment of thecontrol.

While I have shown a particular embodiment of my invention, it will ofcourse be understood that I do not wish to be limited thereto since manymodifications, both in the circuit arrangement and in theinstrumentalities employed, may be made without departing from thespirit and scope of my invention as set forth in the appended claims.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In combination, a signal transmission circuit, means to transmitthrough said circuit audio currents extending over a wide rangeincluding high audio tones and low audio tones, a tone control networkeffective over said wide range and predominately effective in the rangesof said high and low tones, said network comprising a resistance, onepoint of said resistance being connected to one side of said circuitthrough an impedance which is high to low tones andlow to high tones,and another point on said resistance being connected to the same side ofsaid circuit through an impedance which is low to low tones and high tohigh tones, and a connection from the other side of said circuit to apoint on said resistance variable between said first points whereby assaid connection is varied along said resistance opposite effects areproduced upon said high and low tones.

2. In combination, a signal transmission circuit, means to transmitthrough said circuit audio currents extending over a wide rangeincluding high audio tones and low audio tones, atone control networkeffective over said wide range and predominately effective in the rangesof said high and low tones, said network comprising a resistance, onepoint of said resistance being connected to one side of said circuitthrough a capacitance having high impedance to said low tones and lowimpedance to said high tones and another point on said resistance beingconnected to the same side of said circuit through aninductance havinglow impedance to said low tones and high impedance to said high tones,both said inductance and capacitance having values of impedance varyingoppositely with respect to frequency in said frequency range betweensaid high and low tones, and a connection from the other side of saidcircuit to a point on saidresistance variable between said first pointswhereby as said connection is varied along said resistance the frequencyattenuation characteristic of said circuit is correspondingly varied,said variation occurring throughout said range and in opposite senseswith respect to frequency.

3. The combination with an audio frequency transmission circuit, of atone control network connected thereto, said network including aresistor potentiometer having a movable contact, a frequency responsiveimpedancedevice connected between one end of said potentiometer and oneside of said circuit, a second impedance connected between the other endof said potentiometer and the same side of said circuit, and meansconnecting said movable contact of said potentiometer and saidimpedances to the opposite side of said circuit, said impedances beingof such character that said potentiometer operates as a variable controlmeans for said tone control network while maintaining the effectiveohmic load of said network substantially constant.

4. An audio frequency signal transmission circuit including input andoutput circuits, a tone control circuit connected across one of saidcircuitsfor by-passing selected audio frequency energy including aninductive reactance in one path, a capacitive reactance in another path,and a potentiometer having a single movable contact arranged forselectively proportioning the effectiveness of said paths in accordancewith the position of the single movable contact of said potentiometerthereby operates selectively to attenuate the signals in differentfrequency ranges dependent upon the position of said single movablecontact while maintaining a constant ohmic load upon said transmissioncircuit.

5. The combination with an audio frequency current transmission circuitof a tone control network connected in shunt thereto, said networkincluding a resistor potentiometer having a movable contact connected toone side of said circuit, a frequency responsive impedance deviceconnected to one end of said potentiometer, a second impedance devicehaving a resistance value equal to said first impedance and beingconnected to the other end of said potentiometer, both of saidimpedances being connected to the other side of said circuit, saidimpedance devices having different impedance frequency characteristicsand cooperating with said potentiometer to maintain the total apparentvolume of audio frequency current transmitted substantially constant forall of positions of said potentiometercontact.

6; The combination with an audio frequency transmission circuit having asound producing device, of a tone control network connected thereto,said network including a resistor potentiometer having a movablecontact, a frequency responsive impedance device connected between oneend of said potentiometer and one side of said circuit, a secondimpedance having substantially the same ohmic resistance as said firstimpedance device and being connected between the other end of saidpotentiometer and said one side of said circuit, and means connectingsaid movable contact of the potentiometer to the other side of saidcircuit whereby the potentiometer operates as a variable control meansfor said tone control network and said impedances cooperate to maintainthe apparent volume of said sound reproducing device substantiallyconstant for all'adjustments of said potentiometer contact.

7. The combination, in a circuit for transmission of currentsrepresenting music, of a tone control network comprising a plurality ofim pedances including a resistor and a pair of impedances havingdifferent frequency characteristics, one terminal of each of saidimpedances being connected to one side of said circuit and the oppositeterminals of said impedances being connected respectively to oppositeends of said resistor, and a connection from a variable point on saidresistor to the opposite side of said circuit, said impedances being ofsuch character that as said variable point is moved along saidreproduced currents is maintained substantially constant.

8. The combination, in a circuit for transmission of currentsrepresenting music, of a tone control network comprising a plurality ofimpedances including a resistor, and a pair of impedances havingdifierent frequency characteristics, one terminal of each of saidimpedances being connected to one side of said circuit and 5 theopposite terminals of said impedances being connected to opposite endsof said resistor, a connection from a variable point on said resistor tothe opposite side of said circuit, said impedances being of suchcharacter that as said variable point is moved along said resistor thetones efficiently transmitted through said circuit are varied while thetotal volume of reproduced cur- I rents is maintained substantiallyconstant, and

